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SubjectRe: [PATCH v2] cma: make default CMA area size zero for x86
Hello,

On 2014-10-05 15:54, Akinobu Mita wrote:
> This makes CMA memory area size zero for x86 in default configuration
> (doesn't change on the other architectures). If default CMA size is
> zero, DMA_CMA is disabled. It can be enabled by passing cma= to the
> kernel.
>
> This makes less impact on x86. Because there is no mainline driver that
> requires it for x86, and Peter Hurley reported the performance
> regression, as this is trying to drive _all_ dma mapping allocations
> through a _very_ small window.
>
> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> Reported-by: Peter Hurley <peter@hurleysoftware.com>
> Cc: Peter Hurley <peter@hurleysoftware.com>
> Cc: Chuck Ebbert <cebbert.lkml@gmail.com>
> Cc: Jean Delvare <jdelvare@suse.de>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Cc: Don Dutile <ddutile@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Andi Kleen <andi@firstfloor.org>
> Cc: Yinghai Lu <yinghai@kernel.org>
> Cc: x86@kernel.org
> Cc: iommu@lists.linux-foundation.org

Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>

> ---
> * v2
> - Add information in help text, suggested by Chuck Ebbert
>
> drivers/base/Kconfig | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 4e7f0ff..115882f 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -240,18 +240,24 @@ comment "Default contiguous memory area size:"
> config CMA_SIZE_MBYTES
> int "Size in Mega Bytes"
> depends on !CMA_SIZE_SEL_PERCENTAGE
> + default 0 if X86
> default 16
> help
> Defines the size (in MiB) of the default memory area for Contiguous
> - Memory Allocator.
> + Memory Allocator. If the size of 0 is selected, CMA is disabled by
> + default, but it can be enabled by passing cma=size[MG] to the kernel.
> +
>
> config CMA_SIZE_PERCENTAGE
> int "Percentage of total memory"
> depends on !CMA_SIZE_SEL_MBYTES
> + default 0 if X86
> default 10
> help
> Defines the size of the default memory area for Contiguous Memory
> Allocator as a percentage of the total memory in the system.
> + If 0 percent is selected, CMA is disabled by default, but it can be
> + enabled by passing cma=size[MG] to the kernel.
>
> choice
> prompt "Selected region size"

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland



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